Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 214 insertions, 0 deletions

diff --git a/Documentation/spi/pxa2xx.rst b/Documentation/spi/pxa2xx.rst
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+==============================
+PXA2xx SPI on SSP driver HOWTO
+==============================
+
+This a mini HOWTO on the pxa2xx_spi driver. The driver turns a PXA2xx
+synchronous serial port into an SPI master controller
+(see Documentation/spi/spi-summary.rst). The driver has the following features
+
+- Support for any PXA2xx and compatible SSP.
+- SSP PIO and SSP DMA data transfers.
+- External and Internal (SSPFRM) chip selects.
+- Per slave device (chip) configuration.
+- Full suspend, freeze, resume support.
+
+The driver is built around a &struct spi_message FIFO serviced by kernel
+thread. The kernel thread, spi_pump_messages(), drives message FIFO and
+is responsible for queuing SPI transactions and setting up and launching
+the DMA or interrupt driven transfers.
+
+Declaring PXA2xx Master Controllers
+-----------------------------------
+Typically, for a legacy platform, an SPI master is defined in the
+arch/.../mach-*/board-*.c as a "platform device". The master configuration
+is passed to the driver via a table found in include/linux/spi/pxa2xx_spi.h::
+
+  struct pxa2xx_spi_controller {
+	u16 num_chipselect;
+	u8 enable_dma;
+	...
+  };
+
+The "pxa2xx_spi_controller.num_chipselect" field is used to determine the number of
+slave device (chips) attached to this SPI master.
+
+The "pxa2xx_spi_controller.enable_dma" field informs the driver that SSP DMA should
+be used. This caused the driver to acquire two DMA channels: Rx channel and
+Tx channel. The Rx channel has a higher DMA service priority than the Tx channel.
+See the "PXA2xx Developer Manual" section "DMA Controller".
+
+For the new platforms the description of the controller and peripheral devices
+comes from Device Tree or ACPI.
+
+NSSP MASTER SAMPLE
+------------------
+Below is a sample configuration using the PXA255 NSSP for a legacy platform::
+
+  static struct resource pxa_spi_nssp_resources[] = {
+	[0] = {
+		.start	= __PREG(SSCR0_P(2)), /* Start address of NSSP */
+		.end	= __PREG(SSCR0_P(2)) + 0x2c, /* Range of registers */
+		.flags	= IORESOURCE_MEM,
+	},
+	[1] = {
+		.start	= IRQ_NSSP, /* NSSP IRQ */
+		.end	= IRQ_NSSP,
+		.flags	= IORESOURCE_IRQ,
+	},
+  };
+
+  static struct pxa2xx_spi_controller pxa_nssp_master_info = {
+	.num_chipselect = 1, /* Matches the number of chips attached to NSSP */
+	.enable_dma = 1, /* Enables NSSP DMA */
+  };
+
+  static struct platform_device pxa_spi_nssp = {
+	.name = "pxa2xx-spi", /* MUST BE THIS VALUE, so device match driver */
+	.id = 2, /* Bus number, MUST MATCH SSP number 1..n */
+	.resource = pxa_spi_nssp_resources,
+	.num_resources = ARRAY_SIZE(pxa_spi_nssp_resources),
+	.dev = {
+		.platform_data = &pxa_nssp_master_info, /* Passed to driver */
+	},
+  };
+
+  static struct platform_device *devices[] __initdata = {
+	&pxa_spi_nssp,
+  };
+
+  static void __init board_init(void)
+  {
+	(void)platform_add_device(devices, ARRAY_SIZE(devices));
+  }
+
+Declaring Slave Devices
+-----------------------
+Typically, for a legacy platform, each SPI slave (chip) is defined in the
+arch/.../mach-*/board-*.c using the "spi_board_info" structure found in
+"linux/spi/spi.h". See "Documentation/spi/spi-summary.rst" for additional
+information.
+
+Each slave device attached to the PXA must provide slave specific configuration
+information via the structure "pxa2xx_spi_chip" found in
+"include/linux/spi/pxa2xx_spi.h".  The pxa2xx_spi master controller driver
+will uses the configuration whenever the driver communicates with the slave
+device. All fields are optional.
+
+::
+
+  struct pxa2xx_spi_chip {
+	u8 tx_threshold;
+	u8 rx_threshold;
+	u8 dma_burst_size;
+	u32 timeout;
+  };
+
+The "pxa2xx_spi_chip.tx_threshold" and "pxa2xx_spi_chip.rx_threshold" fields are
+used to configure the SSP hardware FIFO. These fields are critical to the
+performance of pxa2xx_spi driver and misconfiguration will result in rx
+FIFO overruns (especially in PIO mode transfers). Good default values are::
+
+	.tx_threshold = 8,
+	.rx_threshold = 8,
+
+The range is 1 to 16 where zero indicates "use default".
+
+The "pxa2xx_spi_chip.dma_burst_size" field is used to configure PXA2xx DMA
+engine and is related the "spi_device.bits_per_word" field.  Read and understand
+the PXA2xx "Developer Manual" sections on the DMA controller and SSP Controllers
+to determine the correct value. An SSP configured for byte-wide transfers would
+use a value of 8. The driver will determine a reasonable default if
+dma_burst_size == 0.
+
+The "pxa2xx_spi_chip.timeout" fields is used to efficiently handle
+trailing bytes in the SSP receiver FIFO. The correct value for this field is
+dependent on the SPI bus speed ("spi_board_info.max_speed_hz") and the specific
+slave device.  Please note that the PXA2xx SSP 1 does not support trailing byte
+timeouts and must busy-wait any trailing bytes.
+
+NOTE: the SPI driver cannot control the chip select if SSPFRM is used, so the
+chipselect is dropped after each spi_transfer.  Most devices need chip select
+asserted around the complete message. Use SSPFRM as a GPIO (through a descriptor)
+to accommodate these chips.
+
+
+NSSP SLAVE SAMPLE
+-----------------
+For a legacy platform or in some other cases, the pxa2xx_spi_chip structure
+is passed to the pxa2xx_spi driver in the "spi_board_info.controller_data"
+field. Below is a sample configuration using the PXA255 NSSP.
+
+::
+
+  static struct pxa2xx_spi_chip cs8415a_chip_info = {
+	.tx_threshold = 8, /* SSP hardward FIFO threshold */
+	.rx_threshold = 8, /* SSP hardward FIFO threshold */
+	.dma_burst_size = 8, /* Byte wide transfers used so 8 byte bursts */
+	.timeout = 235, /* See Intel documentation */
+  };
+
+  static struct pxa2xx_spi_chip cs8405a_chip_info = {
+	.tx_threshold = 8, /* SSP hardward FIFO threshold */
+	.rx_threshold = 8, /* SSP hardward FIFO threshold */
+	.dma_burst_size = 8, /* Byte wide transfers used so 8 byte bursts */
+	.timeout = 235, /* See Intel documentation */
+  };
+
+  static struct spi_board_info streetracer_spi_board_info[] __initdata = {
+	{
+		.modalias = "cs8415a", /* Name of spi_driver for this device */
+		.max_speed_hz = 3686400, /* Run SSP as fast a possbile */
+		.bus_num = 2, /* Framework bus number */
+		.chip_select = 0, /* Framework chip select */
+		.platform_data = NULL; /* No spi_driver specific config */
+		.controller_data = &cs8415a_chip_info, /* Master chip config */
+		.irq = STREETRACER_APCI_IRQ, /* Slave device interrupt */
+	},
+	{
+		.modalias = "cs8405a", /* Name of spi_driver for this device */
+		.max_speed_hz = 3686400, /* Run SSP as fast a possbile */
+		.bus_num = 2, /* Framework bus number */
+		.chip_select = 1, /* Framework chip select */
+		.controller_data = &cs8405a_chip_info, /* Master chip config */
+		.irq = STREETRACER_APCI_IRQ, /* Slave device interrupt */
+	},
+  };
+
+  static void __init streetracer_init(void)
+  {
+	spi_register_board_info(streetracer_spi_board_info,
+				ARRAY_SIZE(streetracer_spi_board_info));
+  }
+
+
+DMA and PIO I/O Support
+-----------------------
+The pxa2xx_spi driver supports both DMA and interrupt driven PIO message
+transfers.  The driver defaults to PIO mode and DMA transfers must be enabled
+by setting the "enable_dma" flag in the "pxa2xx_spi_controller" structure.
+For the newer platforms, that are known to support DMA, the driver will enable
+it automatically and try it first with a possible fallback to PIO. The DMA
+mode supports both coherent and stream based DMA mappings.
+
+The following logic is used to determine the type of I/O to be used on
+a per "spi_transfer" basis::
+
+  if !enable_dma then
+	always use PIO transfers
+
+  if spi_message.len > 8191 then
+	print "rate limited" warning
+	use PIO transfers
+
+  if spi_message.is_dma_mapped and rx_dma_buf != 0 and tx_dma_buf != 0 then
+	use coherent DMA mode
+
+  if rx_buf and tx_buf are aligned on 8 byte boundary then
+	use streaming DMA mode
+
+  otherwise
+	use PIO transfer
+
+THANKS TO
+---------
+David Brownell and others for mentoring the development of this driver.